feat(helm): add Qdrant local mode support with three deployment options [skip ci]

Add support for three Qdrant deployment modes in Helm chart:
1. In-memory mode (:memory:) - Default, zero-config, ephemeral storage
2. Persistent local mode (path-based) - File-based storage with PVC
3. Network mode (URL-based) - Dedicated Qdrant service or external instance

Changes:
- Restructured qdrant configuration in values.yaml with mode selector
- Added conditional environment variable logic in deployment.yaml
- Created PVC template for persistent local mode with optional existingClaim
- Added qdrantPvcName helper template in _helpers.tpl
- Updated README.md with Helm registry URL (https://cbcoutinho.github.io/nextcloud-mcp-server)

Breaking change: Default changed from requiring qdrant.enabled to using
in-memory mode (:memory:) when no Qdrant configuration is provided.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

charts/nextcloud-mcp-server/templates/_helpers.tpl

@@ -94,6 +94,17 @@ Create the name of the PVC to use for OAuth storage
 {{- end }}
 {{- end }}
 
+{{/*
+Create the name of the PVC to use for Qdrant local persistent storage
+*/}}
+{{- define "nextcloud-mcp-server.qdrantPvcName" -}}
+{{- if .Values.qdrant.localPersistence.existingClaim }}
+{{- .Values.qdrant.localPersistence.existingClaim }}
+{{- else }}
+{{- include "nextcloud-mcp-server.fullname" . }}-qdrant-data
+{{- end }}
+{{- end }}
+
 {{/*
 Return the MCP server port
 */}}